You don't go any faster on the downhill, and probably not much faster up.A newbie rider that instead of making 150 watts is now pushing 400+ with no experience gives them speed their bodies are simply incapable of. Steeper learning curve, more panics at higher speeds.
Also, any electric device can be hacked. Want instant on instead of power progression? Sure! Want to deliver 1000 watts instead of a couple hundred? Parts will start showing up as soon as there is a market, it's no different from cars, motorcycle or buying the latest, lightweight carbon wonderparts for your bicycle. The stage is set for a bike to trail become a motorcycle trail. If you want a motorcycle, buy a motorcycle.
It's just easier to go up really steep trails and over technical features.